UPTAKE OF 7,12-DIMETHYLBENZ(A)ANTHRACENE AND BENZO(A)PYRENE IN MELANIN-CONTAINING TISSUES

It is widely accepted that UV exposure is the main etiological factor for malignant melanoma. Epidemiologic studies, however, have indicated that also chemical carcinogens may be a risk factor for the disease. Polycyclic aromatic hydrocarbons such as 7,12-dimethylbenz(a)anthracen e and benzo(a)pyrene represent an important class of carcinogenic chem icals. It is known that 7,12-dimethylbenz(a)anthracene can induce mela notic tumours in various animal species, and human melanocytes in cult ure have been found to be capable of metabolizing benzo(a)pyrene to it s proximate carcinogen benzo(a)pyrene-7,8-diol. In the present study t he disposition of C-14- and H-3-7, 12-dimethylbenz(a)anthracene and C- 14-benzo(a)pyrene was studied in pigmented and albino mice and Syrian golden hamsters by whole-body autoradiography. The results showed pron ounced retention of label in the melanin-containing structures of the eyes and the hair follicles in the pigmented animals. The labelling of the corresponding structures in the albino animals was low. Additiona l experiments showed that 7,12-dimethylbenz(a)anthracene and benzo(a)p yrene as well as some of their metabolites are bound to melanin in vit ro. The specific localization of the polycyclic aromatic hydrocarbons in pigmented tissues due to melanin affinity, combined with bioactivat ing capacity of melanocytes, suggest that these substances may play a role in the induction of malignant melanoma.